Sprayable gypsum plaster composition

ABSTRACT

Fire-retardant coatings for structural metal members are obtained by spraying onto the metal settable plaster compositions which are air-containing pumpable aqueous slurries of compositions consisting essentially of, on a dry weight basis, from 52 to 62 percent calcined gypsum, from 2.5 to 18 percent high wet bulking cellulosic fiber, sufficient foaming agent to achieve good workability and satisfactory pumping characteristics, and enough lightweight aggregate to complete the formula.

United States atent [191 Rothfelder et a1.

1 1 SPRAYABLE GYPSUM PLASTER COMPOSITION [75] Inventors: Raymond E.Rothfelder, Irvine,

Calif; Ralph .I. Bragg, Arlington, Mass.

[73] Assignee: W. R. Grace & (30., Cambridge,

Mass.

Notice: The portion of the term of t his patent subsequent to Mar. 6,1990 has been disclaimed.

122 Filed: 11111. 9, 1973 [21] Appl. No.: 322,271

Related US. Application Data [63] Continuation-impart of Ser. No.122,703, March 10,

1971, Pat. No. 3,719,513.

[52] US. Cl 106/115, 106/109, 106/111 [51] Int. Cl C0411 11/00 [58]Field of Search 106/109, 111-115 [5 6] References Cited UNITED STATESPATENTS 1,423,569 7/1922 Lockhart 106/115 1,954,378 4/1934 Day 106/1152,142,164 l/l939 Young et a1. 52/232 2,322,194 6/1943 King 106/882,485,259 10/1949 Chrislcr 106/114 2,853,394 9/1958 Riddell et a1.106/114 3,042,681 7/1962 Sefton 260/296 Q 3,057,142 10/1962 Cunninghamet a1 106/115 3,153,596 10/1964 Tallentire et a1. 106/115 3,215,54911/1965 Ericson 106/90 2 3,219,112 11/1965 Sauber et al... 106/933,369,929 2/1968 Petersen 106/109 3,376,147 4/1968 Dean 106/109 73,719,513 3/1973 Bragg et a1 106/114 Primary Examiner--I)e1bert E. Gantz7, Assistant ExaminerJohn P. Sheehan Attorney, Agent, or Firm-William L.Baker; C. f Edward Parker ABSTRACT Fire-retardant coatings forstructural metal members 1 are obtained by spraying onto the metalsettable plaster compositions which are air-containing pumpable aqueousslurries of compositions consisting essentially of, on a dry weightbasis, from 52 to 62 percent calcined gypsum, from 2.5 to 18 percenthigh wet bulking cellulosic fiber, sufficient foaming agent to achieve 8Claims, 4 Drawing Figures SPRAYABLE GYPSUM PLASTER COMPOSITIONCROSS-REFERENCES TO RELATED APPLICATIONS This application is acontinuation-in-part of application, Ser. No. 122,703, filed Mar. 10,1971 now US. Pat. No. 3,719,513.

THE PRIOR ART In the course of erecting steel structures, a thickcoating of inorganic material is commonly applied to the metallicstructural elements to achieve a number of objectives including fireretardance, improved appearance and sound deadening. While several typesof formulations have been applied for these purposes over the years bymeans of a variety of techniques, the most successful system so farconsists in spraying onto the steel surfaces settable aqueous mixescomposed essentially of calcined gypsum, a lightweight inorganicmaterial such as exfoliated vermiculite, an inorganic fibrous substance,preferably asbestos, and a foaming agent. A composition of this type isdescribed by Petersen in US. Pat. No. 3,369,929, along with the mostdesirable application technique, i.e., pumping the aqueous mix andspraying it directly onto the steel in one layer.

In order to be suitable for such use, coating mixes, both in the wet anddry state, must possess a number of crucial properties. They must beable to hold the large quantity of water that renders them capable ofbeing pumped easily and to great heights. Yet they must retain aconsistency sufficient to prevent segregation or settling of ingredientsand permit adequate yield or coverage of steel surface at a giventhickness. The coating mixes, furthermore, must obviously adhere tosteel surfaces, both in the slurried state and in the dry state. Also,the mix must set without the undue expansion or shrinkage which'couldonly result in the formation of cracks that would seriously deter fromthe insulative value of the dry coating.

As intimated earlier, this complex balance of properties hassubstantially been achieved heretofore by gypsum-vermiculite mixescontaining asbestos fiber. However, health considerations have recentlycaused the banning of asbestos-containing compositions, thus leaving theindustry without an acceptable substitute. Elimination of the asbestosfrom the type of composition just discussed results in changes inproperties that are sufficiently extensive to render them unsuitable forthe application contemplated.

SUMMARY OF THE INVENTION It has now been discovered settable, sprayableplaster composition yielding satisfactory fire resistance can be made byadding water to a mixture consisting essentially of calcined gypsum, alightweight aggregate material such as exfoliated vermiculite,cellulosic fiber of high wet bulking capacity, and sufficient foamingagent to provide good workability and pumping characteristics. Thecomposition of the invention contains, on a dry basis, about 52 percentto about 62 percent calcined gypsum, about 2.5 percent to about 18percent cellulose fiber, about 0.2 foaming or air-entraining agent, andenough lightweight aggregate to complete the formula.

A cellulosic fiber of high wet bulking capacity is defined, for thepurpose of this invention, as a fibrous cel- DETAILED DESCRIPTION Thefollowing examples are provided to illustrate the compositions of theinvention as well as their excellent properties.

EXAMPLE 1 A settable gypsum plaster composition is prepared by drymixing the following ingredients:

7: By Weight Calcined gypsum 288.3 lbs. 58% No. 3 vermiculite 188.3 lbs.38% Cellulose fiber 19.9 lbs 4% 496.5 lb

To this mixture is added a small quantity of airentraining agent. Inthis instance, this amounts to one pound of technical sodium laurylsulfate.

The vermiculite used in this preparation is a standard grade of expandedmaterial having density of 5.25 pcf. The cellulose fiber is a purifiedunbleached softwood cellulose consisting of over 99.5 percent celluloseand having a particle size distribution such that approximately 33percent of the material is retained on a No. 60 Tyler screen with about33 percent more retained on a No. screen.

The dry mixture just described can be stored until desired. At the pointof use, it is thoroughly admixed with water and is sufficientlyagitated, or otherwise aerated, to provide a slurry of the properconsistency which can then be pumped through spray-application apparatusfor direct spraying onto metal surfaces.

FIRE-RESISTANCE OF PLASTER COMPOSITIONS Fire-resistance classifications,or so-called fire ratings, based on Conditions of Acceptance for floorand roof in the standard for Fire Tests of Building Constructions andMaterials, Underwriters Laboratories 263 (ASTM E119, NFPA 251) have beenobtained for steel structures coated with the plaster of this invention,for example, for coatings on structural steel columns of size WIO 49 andlarger:

Thickness of Coating Duration of Protection 2% inches 4 hrs. 1% inches 3hrs. 1% inches 2 hrs.

This degree of fire resistance which is comparable to that ofasbestos-containing plaster, is rather remarkable on considering thatthe plasters of this invention are formulated with combustible cellulosefibers, a development which contrasts with the trend of the art callingfor employment of inorganic fibrous substances.

, EXAMPLE 2 A conventional asbestos-containing sprayable plastercomposition was prepared essentially as in Example 1, mixed with water,properly aerated, sprayed on steel and allowed to dry and set. The drymix ingredients of this composition were as follows:

A number of properties of coatings obtained from the asbestos-containingcomposition of this example were compared to those of cellulose fiberformulations. It was noted that the latter product generally performsbetter than asbestos formulation.

Specifically, it was determined that on an equal density basis, setcellulose fiber plaster has a greater surface hardness, a higher modulusof elasticity, a lesser thermal conductivity and a smaller volume changeduring setting than comparable conventional asbestos fiber plaster.

These differences in properties and behavior at normal plaster densitiesare illustrated by the accompanying drawings in which FIG. 1 shows themodulus of elasticity,

FIG. 2 shows differences in surface hardness at normal densities,

FIG. 3, the thermal conductivity or K factor, and

FIG. 4, the movement of the plaster mass as it sets.

The modulus of elasticity was determined according to ASTM method C-293.As shown in FIG. 1, the modulus (E) rises from about 5,000 to 1 1,000psi for cellulose fiber-containing plaster over a density range of 19 to23 pcf, a level roughly twice that of asbestos fiber plaster over thesame density range. Inasmuch as a high modulus ultimately contributes tosome extent to hardness of the material, the unexpected increase inmodulus is beneficial for an application such as that to which thecompositions of the invention are destined. Hardness determinationscarried out on the same materials support this improved picture at thedensities tested by revealing essentially a two-fold increase inpenetration resistance (FIG. 2). These penetration resistance valueswere obtained by means of a Soiltest Penetrometer Model C421, using a0.05 square inch needle and a 5 deed welcome. Another greatlyappreciated result of increased surface hardness, both at theconstruction stage and during the entire life of the structure, is thenon-dusting characteristic of the new materials now disclosed.

The trade acceptability of the lightweight organicdemonstrated that. atequal density, cellulosecontaining plaster possesses a lowerconductivity than asbestos plasters (FIG. 3). One can only speculate onthe reasons for this improved value.

FIG. 4 illustrates another important characteristic of lightweightplasters, the volume stability on drying and setting. It is obvious thatwhen volume changes past a certain magnitude, varying degrees ofundesirable results such as cracking peeling, bulging, etc., will occur,with attendant decrease in the utility of the material. On determinationby optical measurement of the volume changes in drying and settingstandard masses (900mm X mm X 20mm bars) of various compositions over aperiod of 9 days, i.e., a period long enough for all movement to cease,it was found that cellulosecontaining plasters are more volume stablethan their asbestos counterpart, both in overall magnitude of volumechange in any direction and in net volume change.

EXAMPLE 3 Kraft process fiber, 20 parts, is suspended in water, 1,050parts, to form a slurry. To this is then added with mixing No. 4expanded vermiculite, 189 parts, CaSO4, 1/2 H 0, 288 parts, and 45percent sodium lauryl sulfate, 1.5 parts.

The Kraft process fiber used here is a cook sulfate originating from ablend of western red cedar, hemlock and spruce. The fibers average 2.70mm in length and a screen analysis reads as follows:

+ 14 mesh 59% weight 28 24 The resulting plaster has a setting time ofabout 3 hours and 20 minutes. It showed an average wet density of 73.12pcf and an average dry density of about 14.6 pcf. The material iscomparable to the plaster of Example l in all respects.

The compositions of the invention, as mentioned earlier, contain gypsumas well as a lighweight aggregate, an organic fibrous material and afoaming agent.

As a lightweight aggregate, there may be used instead of the expandedvermiculite of Example 1, any lightweight inorganic material having adensity within the range of about 4.5 to about 8 pcf. Perlite, clay andslag,

0 in the expanded state, as well as diatomaceous earth are examples ofuseful materials. Vermiculite, however, is preferred not only becausethe intermediate slurries containing it pump best, but also because ofthe greater plaster thickness that can be applied in one pass when it isthe aggregate selected.

The foaming agents or air-entraining agents, that can be used in theformulation of the invention are well known to the art and thus can bedisposed of without too much comment. Suffice it to say that suchmaterials as sulfated monoglycerides, sodium alkyl arylsulfonates ofvarious manufacture, sodium lauryl sulfate and the like are used inquantities sufficient to cause the aqueous slurries to achieve theconsistency needed for pumping and spraying. Obviously, dry foamingagents can be incorporated into the dry gypsum-aggregatefiber mixesbefore dilution with water, while both dry and liquid agents can be usedonce the slurry is made.

In any event, as little'as about 0.5 percent of foaming agent, drybasis, may suffice for a given formulation.

The high wet bulking cellulosic fibrous component of. the plaster of theinvention constituting, as seen earlier; from about 2.5 percent to 18percent of the mix on a dry basis and preferably about 3 to 8 percent,consists of short or chopped organic fibers of natural or syntheticorigin which when incorporated in the composition of the invention,admixed with water, pumped and sprayed, yields at least 24 board feet ofproduct per 50 pounds of dry composition. Board foot (a volumeequivalent to 1 l2 l2) yield of product per pound of dry composition ofthe invention may be determined by intermixing a known quantity of water(in pounds), then after pumping and spraying in the con-l ventionalmanner, obtaining unit weight of the sprayed product and mathematicallycalculating yield. Thus,

Board foot Water (lbs) Dry Wt. (lb Dry Wt. of Comp. (lbs)) X NozzleDensity (lbs per cubic foot) i 12 i l Board foot (per 50 lbs. of drycomposition) 50 wate;0(lbs)) X12 5.5 92 Density flbsreaeuleiebatll J l INozzle density can be readily calculated by one skilled: in this art.For instance, the pumped product as discharged from the nozzle iscollected in a vessel of known volume (for convenience, 1 cubic foot).The net weight of collected product is then measured. From this theweight in pounds, per cubic foot of the collected product is easilydetermined. Usable materials in this class include cellulose fibersgenerally such as wood fiber, sisal, hemp, cotton, jute, ramie, rayonand the like which either possess the required bulking ability naturallyor have acquired it by appropriate physical and chemical modification,for instance, by delignification. A preferred material of this type isthe purified softwood fibers used in Example 1.

In certain instances, it may be desirable to incorporate a smallproportion, say up to about 8 percent, preferably about 0.25 to 1.5percent of inorganic fibers such as glass, Wollastonite, etc., fibers,in the composition of the invention. The following is one example ofsuch a composition:

To this is added the desired amount of air-entraining fagent to completethe formula.

Having thus described the invention, especially in terms of applicationto steel surfaces, is should be noted that the fire resistantcompositions disclosed will also adhere quite well to other commonmaterials, such as wood, cement, brick and the like. It will further be5 apparent to the man skilled in the art that the formula- ,tionsdescribed may be altered to some degree, for ex- ;ample, by the additionthereto of further unspecified ingredients, without departing from thescope of the invention as defined by the following claims.

We claim:

1. A gypsum plaster composition, capable of yielding a settable,sprayable slurry on addition of water, which consists essentially of ona dry weight basis, calcined gypsum, about 52 to 62 percent, high wetbulking cellulosic fiber, about 2.5 to about l8 percent, anairentraining agent, about 0.2 percent, and sufficient lightweightaggregate to complete the formula, said cellulosic fiber havingsufficient wet bulking capacity that when incorporated in the saidcomposition, admixed with water, pumped and sprayed, yields at leastabout .24 board feet of product per 50 pounds of the dry composition.

2. The composition of claim 1 wherein the cellulosic fiber constitutesfrom about 3 to about 8 percent of the dry composition.

3. The composition of claim 2 wherein the cellulosic :fiber is providedby a sulfite pulp.

4. The composition of claim 2 wherein the cellulosic fiber is providedby a kraft pulp.

5. The composition of claim 1 wherein the lightweight aggregate is anexpanded vermiculite having a bulk density within the range of about 4.5to about 8 pcf.

6. The composition of claim 1 wherein the wet bulking capacity of saidcellulosic fiber is sufficient to yield at least about 28 to 32 boardfeetof product.

7. A sprayable, settable plaster slurry consisting of the plastercomposition of claim 1 suspended in water at a level of about 9 to about14 gallons per 50 pounds of dry composition.

8. A fire-retardant set gypsum plaster composition metal structuralassembly consisting of structural metal members coated with thecomposition of claim 6.

1. A GYPSUM PLASTER COMPOSITION, CAPABLE OF YIELDING A SETTABLE,SPRAYING SLURRY ON ADDITION OF WATER, WHICH CONSISTS ESSENTIALLY OF ADRY WEIGHT BASIS, CALCINED GYPSUM, ABOUT 52 TO 62 PERCENT, HIGH WETBULKING CELLULOSIC FIBER, ABOUT 2.5 TO ABOUT 18 PERCENT, ANAIR-ENTRAINING AGENT, ABOUT 0.2 PERCENT, AND SUFFICIENT LIGHTWEIGHTAGGREGATE TO COMPLETE THE FORMULA, SAID CELLULOSIC FIBER HAVINGSUFFICIENT WET BULKING CAPACITY THAT WHEN INCORPORATED IN THE SAIDCOMPOSITION, ADMIXED WITH WATER, PUMPED AND SPRAYED, YIELDS AT LEASTABOUT 24 BOARD FEET OF PRODUCT PER 50 POUNDS OF THE DRY COMPOSITION. 2.The composition of claim 1 wherein the cellulosic fiber constitutes fromabout 3 to about 8 percent of the dry composition.
 3. The composition ofclaim 2 wherein the cellulosic fiber is provided by a sulfite pulp. 4.The composition of claim 2 wherein the cellulosic fiber is provided by akraft pulp.
 5. The composition of claim 1 wherein the lightweightaggregate is an expanded vermiculite having a bulk density within therange of about 4.5 to about 8 pcf.
 6. The composition of claim 1 whereinthe wet bulking capacity of said cellulosic fiber is sufficient to yieldat least about 28 to 32 board feet of product.
 7. A sprayable, settableplaster slurry consisting of the plaster composition of claim 1suspended in water at a level of about 9 to about 14 gallons per 50pounds of dry composition.
 8. A fire-retardant set gypsum plastercomposition metal structural assembly consisting of structural metalmembers coated with the composition of claim 6.